Plasma Display Panels (PDPs) offer promising technology for implementing large, flat video screens. A typical PDP may be formed by enclosing a gas, for example, a mixture of helium and neon between a transparent front panel and a back panel. Electrodes may be routed on the front panel and on the back panel and phosphors may be printed on either the front panel or the back panel. The electrodes are used to ionize the gas, forming a plasma which emits ultraviolet radiation. The ultraviolet radiation, in turn, causes the phosphors to emit visible light. Color displays are made by forming adjacent columns having red, green and blue phosphors, respectively.
A common type of PDP is the three-electrode pulsed Alternating Current (AC) device. In this configuration, each display row includes two parallel row electrodes, for example, on the inside surface of the back panel and each column includes one column electrode, for example, on the inside surface of the front panel. The row electrodes on the back panel may be covered with a dielectric layer so that no direct current (DC) flows between the electrodes when the plasma is ignited. The electrodes on the front panel may also be covered with a dielectric layer.
In order to generate gray-scale values, each field interval of a video image may be divided into multiple sub-field intervals. Each sub-field interval includes a writing phase and an illumination phase. The illumination phases of the different sub-fields of an image field have respective durations. These durations are programmed such that each individual pixel position on the screen may be illuminated for an amount of time proportional to the binary value of an image picture element.
Briefly, an AC plasma display operates as follows. Operation is divided into two phases or states, the writing phase (writing state) and the illumination phase (sustain state). In the writing phase of a given sub-field, data values are written into each pixel position of the display device one row at a time. The rows are selected one at a time by successively applying a select potential to each row. At the same time, voltages are applied to the column electrodes to establish a relatively high potential between the column electrodes and the selected row electrode for pixels that are to be illuminated during the sustain state of the sub-field interval, and to establish a relatively low potential between the column electrodes and the selected row electrode for pixels that are not to be illuminated during the sustain state. The relatively high potential causes an electric charge to be deposited between the front and back panels, on the inside walls of the dielectric layers, at the respective pixel position. This electric charge is commonly known as a "wall charge."
In other words, a pixel which will be bright has a wall charge written into it, and thus receives "ON" data. A pixel which will be dark does not have a wall charge written into it, and thus receives "OFF" data. In some implementations, the writing phase includes a preliminary erase step in which wall charges from the previous frame of data are erased.
After the wall charge has been written for each row of the display, the sustain state of the sub-field begins. During the sustain state a predetermined potential is applied in pulses between the two parallel row electrodes across the entire display. If a pixel position has a wall charge ("ON" data), the predetermined potential ignites the plasma at that pixel position. If the pixel position does not have a wall charge ("OFF" data), the plasma does not ignite.
In conventional PDPs, illumination is prohibited in the writing phase while rows are being written. If illumination is attempted while rows are being written, crosstalk may occur as data voltages on the column electrodes may interfere with the discharge in unselected rows. Thus the display may be relatively dimmer because it is not illuminated while data values are written into the display. In some conventional displays, about 50% of the display time is taken up by the writing phase.
Further, in conventional PDPs, alternating pulses are applied to row electrodes during the illumination phase. Hence, the display generates light as narrow impulses at pulse edges, and each light impulse is allowed to decay fully in order to completely invert the wall charge in preparation for the next pulse. Therefore, the display is dimmer than it would be if light were generated continuously.
Moreover, in a conventional PDP, the use of pulses to write and illuminate the display causes the driver electronics to dissipatively charge and discharge the column and row electrodes. Hence, the power dissipation in conventional PDPs is inefficient.